Scintillation camera with improved resolution

ABSTRACT

An Anger-type scintillation camera system fitted with a gamma ray filter between the object under study and the detector and an output signal filter of the signal funneling type which employs a non-linear array of signal filter windows to compensate for inherent non-linear spatial response characteristics in the camera system.

United States Patent [191 J aszczak 51 Aug. 14, 1973 [5 SCINTILLATIONCAMERA WITH 3,633,031 1 1972 Pence 250/105 3,683,184 8/1972 Brunnett eta1 250/71.5 S IMPROVED RESOLUTION 3,684,886 8/1972 Muehllehner 250/71.5S [75] Inventor: Ronald J. .laszczak, Arlington Heights, 111. PrimaryExaminer-Archle R. Bqgghelt AS51811? sellle & w 3 8 1 Attorney-Lowell C.Bergstedt, Walter C. Ramm 22 Filed: Mar. 10, 1972 at 21 Appl. No.:233,670

[57] ABSTRACT [52] U.S. Cl ..250/368, 250/369 An Angemype scintillationcamera system fitted with 1 Int. Cl. i1. a gamma y filter between theobject under study and [58] Field of Searc 250/715 s, 86, s the detectorand an output signal film 0mm signal mm neling type which employs anon-linear array of signal [56] References Cited filter windows tocompensate for inherent non-linear UN T D STATES PATENTS spatialresponse characteristics in the camera system. 3,631,244 12/1971Bergstedt......... 250/715 S v 5 Claims, 12 Drawing Figures 80 7 50 70;90 PROGRAMABLE 5 DETECTOR DUAL DATA DUAL DE'I ECTOR ELECTRONICS SYSTEMD. AC.

E y H AD GAMMA RAY FILTER r60 COLUMATOR SCAN DRIVES woe AND SIGNAL ROBJECT GENERATORS /30\ UNIFORM GAMMA CAMERA RAY SOURCE PATENTEDMIB 14I913 SHEET 3 BF 3 80 HG. 5 507 707 PRoSRAMABLE (90 DETEc'ToR DuAL' DATADuA'L SAMMA RAY FILTER r60 40 CW scAN DRIVES loo EL-1.1; AND SIGNAL CRTI eENERAToRS OBJECT UNFORM GANWIA /30\CAMERA m RAY SouRcE FIG.6

7 DETEc'ToR DUAL PRGRAMABLE- Du'AL DETECTOR ELECTRONICS A.D.c. DATAD.A.c.

SYSTEM HEAD SAMMA RAY 'coi IMATnR FILTER DEFLEcTIoN 4 gwgw coRREcTIoNcIRcuITRY w SCAN DRIVES AND SIGNAL BOVTCAMERA PRDSRAMASLE DATA F 7['SYSTEM 5 J DETEcToR WM 8%?- L DETEcToR E EcTRoNIcS RECORDEAR HEAD 2oGAMMA RAY FILTER r60 DUAL DQLLIMATDR scAN DRIVES D.A.C.

(:zzzzz- T AND SIGNAL 1 GENERATORS UNIFORM GAMMA 00 RAY SOURCE CAMERA"/30 SCINTILLATION CAMERA WITH IMPROVED RESOLUTION Scintillationcameras, principally Anger-type scintillation cameras, (U. S. Pat. No.3,011,057), are in widespread use in a large number of hospitalsthroughout the United States and foreign countries. These cameras enablephysicians and researchers to visualize static and dynamic distributionsof radioactivity in the human body and thereby obtain useful diagnosticinformation which is often not obtainable with other equipment or isobtainable only at greater expense or greater risk to the patient. Instatic radioactivity imaging of human organs such as the brain, lungs,thyroid, liver, spleen, pancreas, and kidneys, the spatial resolution ofthe scintillation camera is an important parameter in determining thedegree to which structural detail of the organ can be differentiated interms of variations in radioisotope concentrations shown in the imageproduced by the camera. Other important parameters are efficiency (i.e.,the rate of data acquisition), pulse height resolution, linearity, anduniformity of spatial and pulse height resolution and efficiency. Inpractice in design ing a scintillation camera system, trade-offs inthese pa-v rameters must actually be made so that all of them fallwithin acceptable limits, although these limitsare not at presentwell-defined or generally agreed upon. Most of the improvements in thestate of the art of scintillation camera design have been directedtoward improving the spatial resolution while keeping the otherparameters essentially the same or, in some instances, also improvingone or more other parameters.

Larsson U. S. Pat. application Ser. No. 190,618, filed Oct. 19, 1971,discloses an approach to improving the overall spatial resolution of ascintillation camera system which involves the use of a radiation filterbetween the radioactive object being investigated and a radiationsensitive transducer in the detector together with an output signalfilter at the output of the detector. While the embodiments disclosed inthe Larsson patent application are capable of producing asubstantialimprovement in spatial resolution of the camera system, a largesacrifice of sensitivity is involved because the types of output signalfilters employed by Larsson substantially reduce the number ofsdetectedevents which are documented in the final image and'the radiation filteritself also reduces the number of radiation quanta emitted from theobject which are permittedto strike the radiation sensitive transducer.

. Jaszczak U. S. Pat. application Ser. No. 200,700, filed Nov. 20, I971,discloses an improvement to the Larsson-type system which basicallyinvolves the use of the same type of radiation filter but an improvedoutput signal filter of the signal funneling type. The signal fun nelingtype of output signal filter improves the sensitivity of the systembecause essentially all useful interactions in the radiation sensitivetransducer are documented in the final image. The radiation filter andthe output signal filter in the above-referenced Jaszczak applicationhave corresponding regular arrays of windows," that is, the radiationpassageways in the radiation filter are arranged in a regular array andare all the same size and the output signal filter channels or windowsalso comprise a regular array and are all the same size. However,because of the inherent, characteristic non-linear spatial response ofthe camera system, the windows of the output signal filter do notprecisely match the windows of the radiation filter. As a result,sometimes a quantum of radiation which traverses a particular window inthe radiation filter produces output signals which fall within a windowof the output signal filter which is adjacent to the signal filterwindow actually associated with the particular radiation filter window.If the degree of non-linearity of the spatial response of the camerasystem is sufficiently large with respect to the separation betweenadjacent windows of the radiation filter, the misplaced documentation ofevents will cause ghost-type artifacts in the resultant images,especially in locations wherelarge, abrupt variations in concentrationsof radioactive material are present.

Therefore, it is the principal object of this invention to provide animproved apparatus for imaging an object containing a radioactivitydistribution in which the size and placement of output signal filterwindows relative to radiation filter windows is determined in accordancewith the non-linear spatial response of the radiation detector so thatthe respective associated windows are substantially matched.

More specific objects of this invention, and its various features andadvantages will be apparent from a consideration of the followingdetailed description in conjunction with the accompanying drawings inwhich:

FIG. 1 is a plan view of a radiation filter with components of anAnger-type radiation detector shown in phantom lines; v

FIG. 2 is a partly sectioned view of a radiation filter and componentsof an Anger-type radiation detector;

FIGS. 3A and 3B are graphical illustrations useful in explaining thisinvention;

FIG. 4A is a section view of a portion of a radiation filter;

FIGS. 48 to 4E are graphical illustrations useful in explaining thisinvention;

FIG. 5 is a block schematic diagramof one embodi merit of thisinvention;

FIG. 6 is a block schematic diagram of an alternate embodiment of thisinvention; and j 1 FIG. 7 is a block schematic diagram of anotheralternate embodiment of this invention.

Referring to FIGS. 1 and 2, the major components of the detector head 30of an Anger-type'radiation cam era are shown. A scintillation crystal3l,typically in the form of a thin disc of thallium activated sodiumiodide, serves as a radiation sensitive transducer by converting gammarays incident thereon into light flashes. A transparent cover 32 forcrystal 31 and atransparent light pipe 33 conduct the light from crystal31 to photocathodes in nineteen photomultiplier tubes P1 to P19 whichare mounted in a hexagonal array on top of light pipev 33. A radiationfilter 20 having a regular array of square passageways or windows 21 islocated underneath crystal 31. Typically, in practice, a multiaperturegamma ray collimator would be mounted in a fixed position adjacent tocrystal 31 and radiation filter 20 would be movably mounted adjacent tothe collimator. Radiation filter 20 could itself serve as a collimatorprovided its thickness were sufficient to perform the collimationfunction.

FIG. 3A shows the response of an ideal camera sysspacing, and size andshape corresponding to each passageway in radiation filter 20. FIG. 3Bis exemplary of the response of an actual camera. The distributions arenot evenly spaced, the widths and heights of the distributions vary. Itis apparent from FIG. 3B that scintillation events near the central axisof a particular photomultiplier tube tend to produce output signalswhich locate the event as though it has occurred at a position closer tothe tube axis than the actual position. This is an inherentcharacteristic non-linear spatial response of an Anger-type camerasystem. It should be understood that the non-linear response shown inFIG. 3B is an illustrative example of the type of response which mightactually be encountered in practice but the degree and kind ofnon-linearity will vary from one system to another.

FIG. 4A shows a portion of radiation filter 20 and FIGS. 48 and 4Cillustrate a portion of an ideal linear response and a non-linearresponse, respectively. A set of linearly arranged signal filter windowsW1 to W7, i.e., windows of the same width, is appropriate for the caseof an ideal response. However, if signal filter windows W 1 to W7 areused for filtering the non-linear distributions of FIG. 4C, it isapparent, for example, that window W4 will encompass some events whichshould fall in windows W3 and W5. In fact, none of the signal filterwindows W1 to W7 properly encompass the distribution of events relatedto associated passageways in radiation filter 20. The result ofemploying a linear array of signal filter windows to filter signals froma radiation detector having a non-linear spatial response is shown inFIG. 4E. The display intensity levels D1 to D7 associated with signalfilter windows W1 to W7 and corresponding radiation filter passagewaysare of considerably varying height whereas ideally they should all bethe same height.

In accordance with this invention, the non-linear spatial response ofthe radiation detector is compensated for by employing a set of signalfilter windows W1 to W7 which have varying widths. The appropriate widthand position of each signal filter window is determined by digitizingthe output signals from the detector and storing the accumulated eventsin separate memory core locations identified by x and y channel numbers,as shown for the x axis in FIG. 4D. The distribution of stored events isreadily analyzed to ascertain the appropriate channel numbers to beincluded within each signal filter window. Then the events in allchannels within each signal filter window are accumulated and displayedat positions corresponding to coordinates of a central axis of anassociated passageway in radiation filter 20. The result is shown inFIG. 4E as a substantially more uniform set of display distributions D1to D7.

FIG. 4A to 4E illustrate the concepts of this invention in the contextof one dimension, but the extension to two dimensions should beapparent. The preferred approach is to obtain information on theappropriate position and size of each signal filter window whileexposing the radiation detector to a uniform sheet source of gamma raysthrough the radiation filter, as shown for example in FIG. 5. A uniformsheet source of gamma rays 11 (shown in dashed lines) is positionedbeneath gamma ray filter 20. At such time, object would not bepositioned as shown because it would interfere with the, measurements.Gamma ray filter is maintained in one particular position while gammarays from source 11 irradiate the crystal in detector head 30 in aregular pattern through filter 20 and multiaperture collimator 40. Thex,y output signals from detector electronics 50 corresponding to eachevent are digitized by dual analog-to-digital conversion (A.D.C.)circuitry and the resultant digitized signals are stored in a twoparameter matrix of memory storage locations in programable data system80. Storage of events is continued until a statistically adequate numberhas been accumulated. Programable data system then executes anappropriate program to ascertain for each passageway in gamma ray filter20 a unique two parameter set of memory locations in which stored eventswere essentially produced by gamma rays traversing that particularpassageway. Information as to each such set of memory locations isstored in memory together with an identification of the location of thegamma ray filter passageway associated with it. If gamma ray filter 20is to be scanned in relation to object 10 as shown in FIG. 5, it may benecessary to ascertain and store signal filter window information formore than one position of gamma ray filter 20. Once the requiredinformation on appropriate signal filter windows is stored, theapparatus may then be employed to image a radioactivity distribution inobject 10 with uniform gamma ray source 11 removed. Processing of eventscan be accomplished on either a one-event-at-a-time basis or on thebasis of storage of events in a two parameter memory array at eachposition of gamma ray filter 20.

The system shown in FIG. 5 is especially appropriate for processingevents one-at-a-time. For purposes of illustration, assume thatprogramable data system 80 has a two parameter matrix of memorylocations and signal filter window information has been stored thereinin the form of a pair of coordinates in each memory location, thecoordinates being positon coor dinates of a central axis of a particularradiation passageway associated with that memory location as previouslydetermined by measurements using uniform gamma ray source 11. Each setof x,y signals from detector electronics 50 is digitized in dual ADC. 70and the resultant digitized output signals are used to address a uniquememory location in programable data system 80(When a memory location isaddressed, the pair of coordinates stored at that location in digitalform is sent to dual digital-to-analog conversion (D.A.C.) circuitrywhich produces a pair of analog signals which control the location of adisplayed spot on CRT 100. Camera 130 documents the displayed spots onfilm.

Persons skilled in the art will readily appreciate the various ways inwhich the system of FIG. 5 can be modified to process events after theyare cumulatively stored in a matrix of memory locations.

The system of FIG. 6 employs a scanning of object 10 on a support table12 instead of scanning gamma ray filter 20. For this embodiment thefixed relation between gamma ray filter 20 and detector head 30eliminates any need for storing information on multiple sets ofnon-linear signals filter windows. In all other respects its operationis essentially the same as the system in FIG. 5.

The system of FIG. 7 is the same as that of FIG. 5 except the digitizedoutput signals from dual A.D.C. circuitry 70 and the filter positioninformation from scan drives and signal generators 60 is recorded ondigital data recorder for later replay and into programable data system80, for processing. This system is especially useful if storedinformation on signal filter windows needs be altered for variouspositions of gamma ray filter because the data replay can be interruptedwhile the stored information is being changed.

The chief advantages achieved by a system constructed and operated inaccordance with this invention is an improvement in uniformity of thehigh resolution image which is produced by a system employing aradiation filter and an output signal filter.

It should be understood that numerous modifications of embodiments ofthis invention disclosed above could be made without departing from thescope of this invention as claimed in the following claims.

I claim:

1. Apparatus for imaging an object containing a radioactivitydistribution comprising:

a radiation detector of the type which includes a radiation sensitivetransducer and circuit means associated with said transducer forproducing a pair of output signals generally representing spatialcoordinates of interaction of an associated quantum of radiation withsaid transducer, said coordinates being related to a rectangularcoordinate system associated with said transducer, said detector havin ga predetermined resolution value and having an inherent characteristicnon-linear spatial response;

radiation filter means interposed between said transducer and saidobject for defining a two parameter array of mutually spaced radiationpassageways to said transducerfor radiation quanta emitted from saidobject;

a documentation medium;

signal filtering means receiving said pair of output signals operativeto product? on said documentation medium a visual documentation at aposition corresponding to coordinates of a central axis of one of saidradiation passageways traversed by said associated quantum of radiation;and

scanning means for producing relative scanning between said object andsaid radiation filter means and a synchronous relative scanning betweensaid signal filtering means and said documentation medium;

said signal filtering means comprising window circuit means defining atwo parameter array of signal filter windows and a corresponding twoparameter array of associated documentation positions, each of saidsignal filter windows being fitted to output signals associated withquanta of radiation traversing one of said radiation passageways tocompensate for said non-linear spatial response of said radiationimaging apparatus, and each of said documentation positions coincidingwith the coordinates of a central axis of said associated radiationpassageway;

the size and separation distance of said radiation passageways beingpreselected in terms of said resolution value of said detector toproduce a desired value of resolution of the overall apparatus.

2. Apparatus for imaging an object containing a radioactivitydistribution comprising:

a radiation detector of the type which includes a radiation sensitivetransducer and circuit means associated with said transducer forproducing a pair of output electrical signals generally respresentingspatial coordinates of interaction of a quantum of radiation with saidtransducer, said coordinates being related to a rectangular coordinatesystem associated with said transducer, said detector having apredetermined resolution value and having an inherent characteristicnon-linear spatial response;

radiation filter means interposed between said transducer and saidobject for defining a two parameter array of mutually spaced radiationpassageways to said transducer for radiation quanta emitted from saidobject;

signal filtering means receiving said pair of output electrical signalsoperative to produce a pair of filtered output signals representingposition coordinates of a central axis of a particular one of saidradiation passageways traversed by said quantum of radiation;

documenting means receiving said pair of filtered output signalsoperative to document said signals in the form of a spatially locatedvisible spot; and

scanning means for producing relative scanning be tween said object andsaid radiation filter means and a synchronous relative scanning betweensaid signal filtering means and said documenting means;

the size and separation distance of said radiation passageways beingpreselected in terms of said resolution value of said detector toproduce a desired value of resolution of the overall apparatus;

said signal filtering means comprising:

means for digitizing each of said output electrical signals into one ofa number of digital signal levels and producing a pair of digitizedoutput signals, said number of digitized signal levels being at leastseveral times greater than the greater number of radiation passagewaysalong the axes of said rectangular coordinate system; and

means for defining a unique two parameter set of digitized signal levelsassociated with each of said radiation passageways in accordance withsaid nonlinear spatial response of said radiation imaging apparatus andoperative in response to a pair of digitized output signals associatedwith a particular two parameter set to produce said pair of filteredoutput signals.

3. Apparatus as claimed in claim 2, wherein said means for digitizingcomprises a pair of analog-todigital converters each receiving one of.said output electrical signals and producing a pair of digital wordseach comprising a particular channel address; and wherein said means fordefining comprises:

storage means for storing a set of pairs of channel addresses associatedwith each of said radiation passageways; and

processor means receiving said pair of digital words and communicatingwith said storage means operative to determine a particular setassociated with said pair of digital words and to produce said pair offiltered output signals representing the position coordinates of acentral axis of a particular radiation passageway associated with saidset; I

said storage of a set of pairs of channel addresses associated with eachof said radiation passageways being based on measurements previouslyperformed with said radiation imaging apparatus exposed through saidradiation filter means to a substantially uniform radiation source,whereby each set of pairs of channel addresses is corrected for saidcharacteristic non-linear spatial response of said radiation detector.4. Apparatus for imaging an object containing a radioactivitydistribution comprising a radiation detector of the type which includesa radiation sensitive transducer and circuit means associated with saidtransducer for producing a pair of output signals generally representingspatial coordinates of interaction of an associated quantum of radiationwith said transducer, said coordinates being related to a rectangularcoordinate system associated with said transducer, said apparatus havinga predetermined resolution value and having an inherent characteristicnon-linear spatial response;

a radiation filter interposed between said transducer and said objectfor defining a two parameter array of mutually spaced radiationpassageways to said transducer for radiation quanta emitted from saidobject;

drive means for scanning said radiation filter stepwise in a rectilinearraster and producing a pair of filter position signals;

a pair of analog-to-digital converters receiving said pair of outputsignals and producing a pair of digitized output signals;

storage means for storing each said pair of digitized output signals asan accumulated event at an appropriate location in a two parameter arrayof storage elements;

memory means for storing a set of window parameters each correspondingto one of said radiation passageways in at least one position of saidradiation filter, said parameters being predetermined in accordance withsaid non-linear spatial response of said radiation imaging apparatus;

a display means;

processor means receiving said pair of filter position signals operativeto accumulate events in said storage means within each of said storedwindow parameters and to display said accumulated events on said displaymeans at a position corresponding to coordinates of central axes ofassociated radiation passageways;

the size and separation distance of said radiation passageways beingpreselected in terms of said resolution value of said detector toproduce a desired value of resolution of the overall apparatus. 5.Apparatus for imaging an object containing a radioactivity distributioncomprising:

a radiation detector of the type which includes a radiation sensitivetransducer and circuit means associated with said transducer forproducing a pair of output signals generally representing spatialcoordinates of interaction of an associated quantum of radiation withsaid transducer, said coordinates being related to a rectangularcoordinate system associated with said transducer, said apparatus havinga predetermined resolution value and having an inherent characteristicnon-linear spatial response;

a radiation filter interposed between said transducer and said objectfor defining a two parameter array of mutually spaced radiationpassageways to said transducer for radiation quanta emitted from saidobject;

a pair of analog-to-digital converters receiving said pair of outputsignals and producing a pair of digitized output signals;

storage means for storing each said pair of digitized output signals asan accumulated event at an appropriate location in a two parameter arrayof storage elements;

memory means for storing a set of window parameters each correspondingto one of said radiation passageways, said parameters beingpredetermined in accordance with said non-linear spatial response ofsaid radiation imaging apparatus;

a display means;

processor means for accumulating events in said storage means withineach of said stored window parameters and displaying said accumulatedevents on said display means at positions corresponding to coordinatesof central axes of associated radiation passageways;

scanning means for scanning said object in relation to said radiationfilter and synchronously scanning said display means;

the size and separation distance of said radiation passageways beingpreselected in terms of said resolution value of said detector toproduce a desired value of resolution of the overall apparatus. a

1. Apparatus for imaging an object containing a radioactivitydistribution comprising: a radiation detector of the type which includesa radiation sensitive transducer and circuit means associated with saidtransducer for producing a pair of output signals generally representingspatial coordinates of interaction of an associated quantum of radiationwith said transducer, said coordinates being related to a rectangularcoordinate system associated with said transducer, said detector havinga predetermined resolution value and having an inherent characteristicnon-linear spatial response; radiation filter means interposed betweensaid transducer and said object for defining a two parameter array ofmutually spaced radiation passageways to said transducer for radiationquanta emitted from said object; a documentation medium; signalfiltering means receiving said pair of output signals operative toproduce on said documentation medium a visual documentation at aposition corresponding to coordinates of a central axis of one of saidradiation passageways traversed by said associated quantum of radiation;and scanning means for producing relative scanning between said objectand said radiation filter means and a synchronous relative scanningbetween said signal filtering means and said documentation medium; saidsignal filtering means comprising window circuit means defining a twoparameter array of signal filter windows and a corresponding twoparameter array of associated documentation positions, each of saidsignal filter windows being fitted to output signals associated withquanta of radiation traversing one of said radiation passageways tocompensate for said nonlinear spatial response of said radiation imagingapparatus, and each of said documentation positions coinciding with thecoordinates of a central axis of said associated radiation passageway;the size and separation distance of said radiation passageways beingpreselected in terms of said resolution value of said detector toproduce a desired value of resolution of the overall apparatus. 2.Apparatus for imaging an object containing a radioactivity distributioncomprising: a radiation detector of the type which includes a radiationsensitive transducer and circuit means associated with said transducerfor producing a pair of output electrical signals generallyrespresenting spatial coordinates of interaction of a quantum ofradiation with said transducer, said coordinates being related to arectangular coordinate system associated with said transducer, saiddetector having a predetermined resolution value and having an inherentcharacteristic non-linear spatial response; radiation filter meansinterposed between said transducer and said object for defining a twoparameter array of mutually spaced radiation passageways to saidtransducer for radiation quanta emitted from said object; signalfiltering means receiving said pair of output electrical signalsoperative to produce a pair of filtered output signals representingposition coordinates of a central axis of a particular one of saidradiation passageways traversed by said quantum of radiation;documenting means receiving said pair of filtered output signalsoperative to document said signals in the form of a spatially locatedvisible spot; and scanning means for producing relative scanning betweensaid object and said radiation filter means and a synchronous relativescanning between said signal filtering means and said documenting means;the size and separation distance of said radiation passageways beingpreselected in terms of said resolution value of said detector toproduce a desired value of resolution of the overall apparatus; saidsignal filtering means comprising: means for digitizing each of saidoutput electrical signals into one of a number of digital signal levelsand producing a pair of digitized output signals, said number ofdigitized signal levels being at least several times greater than thegreater number of radiation passageways along the axes of saidrectangular coordinate system; and means for defining a unique twoparameter set of digitized signal levels associated with each of saidradiation passageways in accordance with said non-linear spatialresponse of said radiation imaging apparAtus and operative in responseto a pair of digitized output signals associated with a particular twoparameter set to produce said pair of filtered output signals. 3.Apparatus as claimed in claim 2, wherein said means for digitizingcomprises a pair of analog-to-digital converters each receiving one ofsaid output electrical signals and producing a pair of digital wordseach comprising a particular channel address; and wherein said means fordefining comprises: storage means for storing a set of pairs of channeladdresses associated with each of said radiation passageways; andprocessor means receiving said pair of digital words and communicatingwith said storage means operative to determine a particular setassociated with said pair of digital words and to produce said pair offiltered output signals representing the position coordinates of acentral axis of a particular radiation passageway associated with saidset; said storage of a set of pairs of channel addresses associated witheach of said radiation passageways being based on measurementspreviously performed with said radiation imaging apparatus exposedthrough said radiation filter means to a substantially uniform radiationsource, whereby each set of pairs of channel addresses is corrected forsaid characteristic non-linear spatial response of said radiationdetector.
 4. Apparatus for imaging an object containing a radioactivitydistribution comprising a radiation detector of the type which includesa radiation sensitive transducer and circuit means associated with saidtransducer for producing a pair of output signals generally representingspatial coordinates of interaction of an associated quantum of radiationwith said transducer, said coordinates being related to a rectangularcoordinate system associated with said transducer, said apparatus havinga predetermined resolution value and having an inherent characteristicnon-linear spatial response; a radiation filter interposed between saidtransducer and said object for defining a two parameter array ofmutually spaced radiation passageways to said transducer for radiationquanta emitted from said object; drive means for scanning said radiationfilter stepwise in a rectilinear raster and producing a pair of filterposition signals; a pair of analog-to-digital converters receiving saidpair of output signals and producing a pair of digitized output signals;storage means for storing each said pair of digitized output signals asan accumulated event at an appropriate location in a two parameter arrayof storage elements; memory means for storing a set of window parameterseach corresponding to one of said radiation passageways in at least oneposition of said radiation filter, said parameters being predeterminedin accordance with said non-linear spatial response of said radiationimaging apparatus; a display means; processor means receiving said pairof filter position signals operative to accumulate events in saidstorage means within each of said stored window parameters and todisplay said accumulated events on said display means at a positioncorresponding to coordinates of central axes of associated radiationpassageways; the size and separation distance of said radiationpassageways being preselected in terms of said resolution value of saiddetector to produce a desired value of resolution of the overallapparatus.
 5. Apparatus for imaging an object containing a radioactivitydistribution comprising: a radiation detector of the type which includesa radiation sensitive transducer and circuit means associated with saidtransducer for producing a pair of output signals generally representingspatial coordinates of interaction of an associated quantum of radiationwith said transducer, said coordinates being related to a rectangularcoordinate system associated with said transducer, said apparatus havinga predetermined resolution value and having an inherent characteristicnon-linEar spatial response; a radiation filter interposed between saidtransducer and said object for defining a two parameter array ofmutually spaced radiation passageways to said transducer for radiationquanta emitted from said object; a pair of analog-to-digital convertersreceiving said pair of output signals and producing a pair of digitizedoutput signals; storage means for storing each said pair of digitizedoutput signals as an accumulated event at an appropriate location in atwo parameter array of storage elements; memory means for storing a setof window parameters each corresponding to one of said radiationpassageways, said parameters being predetermined in accordance with saidnon-linear spatial response of said radiation imaging apparatus; adisplay means; processor means for accumulating events in said storagemeans within each of said stored window parameters and displaying saidaccumulated events on said display means at positions corresponding tocoordinates of central axes of associated radiation passageways;scanning means for scanning said object in relation to said radiationfilter and synchronously scanning said display means; the size andseparation distance of said radiation passageways being preselected interms of said resolution value of said detector to produce a desiredvalue of resolution of the overall apparatus.